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Expand FMT_FORMAT_AS to include implicit conversions (#4055)

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Allows (for example) types convertible to std::string_view to inherit
from the fmt::formatter<fmt::string_view> to work etc.
This commit is contained in:
Justin Riddell 2024-07-14 17:51:49 +01:00 committed by GitHub
parent c9102619da
commit 5ef93a9f80
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2 changed files with 23 additions and 3 deletions
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12
include/fmt/format.h
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@ -3976,9 +3976,15 @@ struct formatter<T, Char, enable_if_t<detail::has_format_as<T>::value>>
}
};
#define FMT_FORMAT_AS(Type, Base) \
template <typename Char> \
struct formatter<Type, Char> : formatter<Base, Char> {}
#define FMT_FORMAT_AS(Type, Base) \
template <typename Char> \
struct formatter<Type, Char> : formatter<Base, Char> { \
template <typename FormatContext> \
auto format(Type value, FormatContext& ctx) const -> decltype(ctx.out()) { \
using base = formatter<Base, Char>; \
return base::format(value, ctx); \
} \
}
FMT_FORMAT_AS(signed char, int);
FMT_FORMAT_AS(unsigned char, unsigned);

14
test/format-test.cc
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@ -1650,6 +1650,20 @@ TEST(format_test, format_explicitly_convertible_to_std_string_view) {
EXPECT_EQ("'foo'",
fmt::format("{}", explicitly_convertible_to_std_string_view()));
}
struct convertible_to_std_string_view {
operator std::string_view() const noexcept { return "Hi there"; }
};
FMT_BEGIN_NAMESPACE
template <>
class formatter<convertible_to_std_string_view>
: public formatter<std::string_view> {};
FMT_END_NAMESPACE
TEST(format_test, format_implicitly_convertible_and_inherits_string_view) {
static_assert(fmt::is_formattable<convertible_to_std_string_view>{}, "");
EXPECT_EQ("Hi there", fmt::format("{}", convertible_to_std_string_view{}));
}
#endif
class Answer {};